AGTA GTC Laboratory Update
Nov 5, 2008
In this message…
Lab alert about synthetic red spinel
In their latest October Newsletter, SSEF Swiss Gemmological Institute describes the recent occurrence of flux-grown synthetic red spinel, probably due to the popularity of natural red spinel.
Traditional gemological methods cannot be used to distinguish flux-grown synthetic spinel from natural spinel as the RI and SG are the same and the spectrum in the spectroscope looks the same. Even rough crystals look the same (see photo). Some indications can be found in the microscope: Flux synthetic spinels generally only show few inclusions, mainly jagged flux residue, metallic flakes, and tiny parallel hollow channels. Natural red spinel is often quite included with healed fissures consisting of octahedral negative crystals.
Chemical and Raman analysis usually helps to distinguish between the two if microscopic evidence is not enough.
For the full article from SSEF, please go to http://www.ssef.ch/en/news/pdf/08-10_newsletter_spinel.pdf.
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Fig. 1:
Faceted and rough flux synthetic spinels. The octahedral crystals have been produced in Russia in the early 90’s. Photo:M.S. Krzemnicki; © SSEF 2008 |
Prepare for the Holiday Season
The holiday season is approaching fast. A great sales tool for high-end gemstones is the JewelFolio, a 32-44 page fully customized book to accompany your gemstone.
JewelFolios are only issued for Burma rubies, Burma sapphires, Kashmir sapphires, Sri Lanka sapphires, Colombian emerald, and tanzanite. The pages are filled with history and lore, photos of the mines, the AGTA Origin Report, which includes the specific data on the gemstone, including an inclusion photo and spectra.
Dyed Corundum
Recently, the AGTA GTC received some small beads in red, green and blue. Microscopic observation showed a highly fractured material with dye in the fissures. The refractive index could not be measured due to the uneven surface, and a specific gravity could not be taken because the beads were very small. However, EDXRF revealed a chemistry consistent with corundum and the Raman spectrum showed typical corundum peaks together with peaks that we know from artificial dyes. We thought that this may be some old material because of the rough surface. However, shortly thereafter, we received a bracelet with the same type of material (Fig. 1).
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Fig. 2 Photo:L Kiefert; ©AGTA GTC |
The bracelet showed four red, two blue, and two green pear-shaped gemstones of approximately 12 mm in length set in a closed back mounting. When viewed in the microscope, we could see that the material was identical to the one in the previously-discussed small beads - a highly fractured white material with the fractures mainly following twin planes. In the fractures, color concentrations could be observed (Fig. 2 ). The inclusions were intact and unaltered by heat. Qualitative analysis with EDXRF showed some additional elements such as Si, indicating that the dye could be in glass. However, Raman analysis on the broad fractures with lower hardness and reflection revealed only the dye without any other additional peaks, as would be expected from a different material. To make sure that was not the case, we then took a spot analysis with EDXRF on the broad fracture. EDXRF only showed corundum without any other elements. These results indicated that the material was indeed only dyed corundum without any additional glass.
